A portable information device such as a mobile telephone or PDA (Personal Digital Assistant) usually has a display panel for displaying information and a circuit (a driver IC) for driving the display panel, which is formed by a semiconductor integrated circuit (IC). A portable information device uses a comparatively low-voltage battery as an external power supply, but the display panel usually requires a voltage higher than that of the supply voltage of the battery. For this reason, the driver IC generally incorporates a power supply circuit for generating the necessary driving voltage by boosting the supply voltage.
An example of such a power supply circuit is illustrated in Patent Document 1. Specifically, as shown in FIG. 1, a power supply circuit 1 of charge-pump type has a charge pump 10 and a regulator 20. With this arrangement, the pulses of a clock signal CLK1 that causes the charge pump 10 to perform a boosting operation are skipped by the regulator 20 in accordance with the output voltage of the charge pump 10, whereby a voltage (a target voltage) obtained by boosting supply voltage VDD up to a desired voltage value is output from the charge pump 10 as Vout. A detailed description of the structure and operation of the charge pump 10 and regulator 20 are set forth in Patent Document 1 and are omitted here.
[Patent Document 1]
Japanese Patent Kokai Publication No. JP-P2005-20971A (FIGS. 3, 4)